全文获取类型
收费全文 | 18239篇 |
免费 | 3942篇 |
国内免费 | 5390篇 |
专业分类
测绘学 | 2322篇 |
大气科学 | 3005篇 |
地球物理 | 3932篇 |
地质学 | 10557篇 |
海洋学 | 2614篇 |
天文学 | 555篇 |
综合类 | 2046篇 |
自然地理 | 2540篇 |
出版年
2024年 | 126篇 |
2023年 | 376篇 |
2022年 | 1012篇 |
2021年 | 1201篇 |
2020年 | 988篇 |
2019年 | 1112篇 |
2018年 | 1286篇 |
2017年 | 1073篇 |
2016年 | 1185篇 |
2015年 | 1235篇 |
2014年 | 1373篇 |
2013年 | 1449篇 |
2012年 | 1525篇 |
2011年 | 1521篇 |
2010年 | 1498篇 |
2009年 | 1347篇 |
2008年 | 1188篇 |
2007年 | 1109篇 |
2006年 | 956篇 |
2005年 | 794篇 |
2004年 | 566篇 |
2003年 | 494篇 |
2002年 | 477篇 |
2001年 | 492篇 |
2000年 | 463篇 |
1999年 | 479篇 |
1998年 | 318篇 |
1997年 | 309篇 |
1996年 | 276篇 |
1995年 | 219篇 |
1994年 | 257篇 |
1993年 | 181篇 |
1992年 | 143篇 |
1991年 | 107篇 |
1990年 | 75篇 |
1989年 | 54篇 |
1988年 | 67篇 |
1987年 | 49篇 |
1986年 | 35篇 |
1985年 | 34篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1976年 | 7篇 |
1958年 | 11篇 |
1957年 | 7篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 147 毫秒
421.
According to calculation results of ocean chlorophyll concentration based on SeaWiFS data by SeaBAM model and synchronous ship-measured data, this research set up an improved model for CaseⅠand CaseⅡwater bodies respectively. The monthly chlorophyll distribution in the East China Sea in 1998 was obtained from this improved model on calculation results of SeaBAM. The euphotic depth distribution in 1998 in the East China Sea is calculated by using remote sensing data of K490 from SeaWiFS according to the relation between the euphotic depth and the oceanic diffuse attenuation coefficient. With data of ocean chlorophyll concentration, euphotic depth, ocean surface photosynthetic available radiation (PAR), daily photoperiod and optimal rate of daily carbon fixation within a water column, the monthly and annual primary productivity spatio-temporal distributions in the East China Sea in 1998 were obtained based on VGPM model. Based on analysis of those distributions, the conclusion can be drawn that there is a clear bimodality character of primary productivity in the monthly distribution in the East China Sea. In detail, the monthly distribution of primary productivity stays the lowest level in winter and rises rapidly to the peak in spring. It gets down a little in summer, and gets up a little in autumn. The daily average of primary productivity in the whole East China Sea is 560.03 mg/m2/d, which is far higher than the average of subtropical ocean areas. The annual average of primary productivity is 236.95 g/m2/a. The research on the seasonal variety mechanism of primary productivity shows that several factors that affect the spatio-temporal distribution may include the chlorophyll concentration distribution, temperature condition, the Yangtze River diluted water variety, the euphotic depth, ocean current variety, etc. But the main influencing factors may be different in each local sea area. 相似文献
422.
Red tides are one of the main coastal catastrophic events in Guangdong Province of southern China. The comparison between the number of red tide events and the development indexes of cities along the coasts of the province shows that the regional differences in red tide outbreaks has close relations with the coastal urban developments. The cause for an initiation of red tide blooms may be natural factors, while wastewater caused by the fast development of population, industry and aquiculture of the coastal cities enhanced the blooms. It may explain why the two periods of frequent outbreaks of the red tides over the last two decades matched the urban developments in the coastal areas of Guangdong not only spatially but also temporally. The red tides in the first period were restricted only to the coasts of middle Guangdong, where urbanization process was at a higher speed than the other coastal areas of the province. In the second period, fast development of the coastal cities in eastern Guangdong led to an increase in the occurrence of red tides in local sea areas of the same coasts. 相似文献
423.
424.
山西大同-阳高地震活动背景 总被引:2,自引:1,他引:2
通过对大同盆地历史地震活动及大同盆地历史地震活动与华北地震区、山西地震带强震活动的关系的研究,得出山西大同-阳高1989年6.1级地震活动是这一地区历史地震的延续,是华北北部中强地震活动的重要组成部分,具有广义前震的重要意义,其后对应发生的河北张北6.2级地震。标志着华北地震区的地震活动期已进入尾声。 相似文献
425.
426.
Introduction The Great North China, located at longitude 106E to 124E and latitude 31N to 42N, in-cludes three secondary active tectonic blocks, Ordos, Yanshan and North China plain (Figure 1). The geological tectonics of these three secondary blocks is much different from each other. As a stable block with high rigidity, the Ordos block is mostly surrounded by down-faulted basins with an inactive interior since Cenozoic, although the fault zones along its boundary are strongly active wi… 相似文献
427.
Introduction The Xiuyan earthquake(MS=5.4)on Nov.29,1999,occurred between Hushan town and Pi-anling town at the southeast end of the aftershocks of Haicheng earthquake(MS=7.3).These two earthquakes′sequences are highly similar in the way that the foreshocks are very frequent,focal mechanisms of the main shocks are about the same and fault strikes are approximately in the same direction.It is important to study these earthquakes for further research on seismogenesis to fore-cast earthquake… 相似文献
428.
Introduction Data mining (SHAO and YU, 2003) is a new kind of technique developed with database and artificial intelligence in recent years, which processes the data in the database to abstract the im- plied and pre-unknown, but potentially useful information and knowledge from large amounts of incomplete, noisy, blurring and stochastic data. For data mining, data purging is an important link beforehand that includes eliminating noise, making up lost domain, and deleting ineffective data, as… 相似文献
429.
WU Yaping ZHU Yuanlin GUO Chunxiang SU Qiang & MA Wei . School of Civil Engineering Lanzhou Jiaotong University Lanzhou China . State Key Laboratory of Frozen Soil Engineering Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2005,48(7)
In the construction of Qinghai-Tibet railway,to avoid diseases caused by frost heave and thaw col-lapse of frozen ground,besides the normal bridges over the rivers,a lot of dry bridge structures have been built to replace subgrade in the regions of high tem-perature and high ice content frozen soil.So,the problems on forming mechanism of bearing capacity of pile foundation in cold regions already become one of hot spot problems in frozen soil engineering.Freezing force and frost heave force ar… 相似文献
430.
Mesozoic-Cenozoic tectonic transition in Kuqa Depression-Tianshan, Northwest China: Evidence from sandstone detrital and geochemical records 总被引:2,自引:0,他引:2
LI Zhong GUO Hong WANG Daoxuan & LIN Wei . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Tarim Oilfield Branch CNPC Korla China . Hefei University of Industry Tunxilu Hefei China 《中国科学D辑(英文版)》2005,48(9):1387-1402
Succeeding to multiply collisions of different blocks in Late Paleozoic[1―5], complex intracontinental structural deformation occurred in the Tianshan area during Mesozoic-Cenozoic[6―16], which controlled coeval basin-range evolution and resulted in intensive modi- fication and adjustment of the Paleozoic oil-gas reser- voirs[17―19]. The Kuqa Depression is a secendary struc- tural unit of the Tarim basin, in which Mesozoic- Ce- nozoic deposits occur in thickness of 6000―7000 m. The Kuq… 相似文献